Whether a boy will grow taller at 18 depends on whether his epiphysis is closed or not, and is also related to his general condition, genetic factors, the time when puberty begins, and how he develops. If a boy’s epiphyses are not closed, he can still grow taller. Most boys’ epiphyses basically close at 18 years of age and they will not grow any taller. However, there are individual differences. Some boys start puberty later and their epiphyses close later, so they may grow again. If the epiphyses are not closed, supplementing adequate nutrition, exercising, and getting enough sleep, it is possible to grow taller after the age of 18. The final adult height depends on genetic factors, which account for 70% to 80% of the total.